1. Field of the Invention
The present invention relates to a method for manufacturing a gate electrode and a method for manufacturing a semiconductor device, which make it possible to manufacture efficiently a fine gate electrode, and relates to a gate electrode and a semiconductor device manufactured by the method for manufacturing a gate electrode and the method for manufacturing a semiconductor device.
2. Description of the Related Art
A field-effect transistor with excellent high frequency properties is useful for a transmitting and receiving device of quasi-millimeter and millimeter band waves and a high-speed signal processing (optical communication) device. In the developments of the gate electrode used for the device, particularly in which excellent high frequency properties are required, up to now there has been extensive effort on making the gate forming aperture as fine as possible and the gate length as short as possible. As a means for making the gate forming aperture finer, the following have been developed (Japanese Patent Application Laid-Open UP-A) No. 2001-19860 and JP-A No. 2004-87967),    (1) a method in which drawing is carried out in fine detail by shortening the exposure source wave length for drawing or refining the electron beam diameter,    (2) a method in which the opening dimensions are reduced by thermosoftening according to the heat-treatment of the resist making the gate forming aperture,    (3) a method in which the opening dimensions are reduced by heat treatment after the part around the gate electrode forming aperture, which forms the gate forming aperture, is thickened by irradiating an electron beam.
However, there are the following problems in these methods. Namely, in the case of the (1), the exposure device and the mask is expensive in price, causing the entire cost for manufacturing to be expensive. In the case of the (3), it is not suited for mass-production from the viewpoints of throughput and safety because the method uses an electron beam. On the other hand, in the case of the above-mentioned (2), because the amount of the reduction of the opening dimensions obtained stably is about 0.04 μm or less, reducing the opening dimensions drastically beyond this creates problems in the uniformity, and is not suited for mass-production.
An object of the present invention is to solve the problems in conventional technologies and provide a method for manufacturing a gate electrode and a method for manufacturing a semiconductor device, which make it possible to manufacture a fine gate electrode efficiently, by thickening the gate electrode aperture formed by regular ultraviolet exposure and by reducing the opening dimensions, and to provide a gate electrode and a high quality semiconductor device with the gate electrode being suited for a field-effect transistor which has excellent high frequency properties and is useful for a transmitting and receiving device of quasi-millimeter and millimeter band waves and a high-speed signal processing (optical communication) device.